This invention relates to a piezo-electric push button switch in which an electromotive force generated by distorting the piezo-electric plate is employed as a switching signal.
In a conventional push button switch of this type, the click operation of a plunger is obtained by utilizing a force of attraction between the plunger and a permanent magnet which is mounted on a housing. However, the push button switch is disadvantageous in that owing to the above-described arrangement, it is difficult to miniaturize the switch and the switch itself has a high manufacturing cost.
Furthermore, the conventional push button switch of this type suffers from a drawback that, because the piezo-electric plate or leads fixedly secured to the piezo-electric plate are secured directly to the housing, external impact on or vibration of the housing or the terminals is transmitted to the piezo-electric plate so as to generate an electromotive force, so that the switch may be erroneously operated.
When the output of the piezo-electric switch is taken out as it is and is amplified, the output thus amplified includes a number of harmonics, thus showing a number of peaks. Accordingly, the apparent characteristic of the switch is such that the switch undergoes chattering or bouncing. Therefore, heretofore, a load resistor has been connected through an integration circuit consisting of a series resistor and a parallel capacitor, which is provided outside of the switch, so that the output of the piezo-electric plate is supplied to the amplifier after being converted into a signal having a single peak.